Tyres affect mpg?

[niro tyro]

I bought a new-model Niro 4 hybrid in September with 18in wheels. It replaced an old-model Niro 3 with 16in wheels. With my old model I was getting mpg in the low/mid 60s, often 70-plus. With my new Niro I’m averaging mpg in the low 50s – or less – driving the same roads in the same way in the same eco mode. Obviously the tyres on the 18in wheels are lower profile with a wider footprint. The 16in tyres on my old Niro were energy-savers with a narrower footprint. And I’ve noticed mpg is a little lower in winter. But can the difference in tyres alone account for the inferior mpg I’m getting?
Also – The 16in wheels on my old Niro gave a MUCH more comfortable ride than the 18s I have now. But I was told the new Niro 4 hybrid isn’t available with 16in wheels. With low profile tyres, sharper styling and the option of contrasting C pillars, it looks like Kia is trying to appeal to a younger cross-section of drivers. But am I the only one who thinks they shot themselves in the foot by not offering 16in wheels as an option for drivers like me who prefer a more comfortable ride?

[Rucksack52]

I have the same vehicle as you. I am an older person who doesn't drive like a maniac.. my milage is not as good as yours. I reset the trip at every fill up. With 1/2 a tank gone mine shows 45.4 mpg average. With only 4400 miles done since I got the car it shows 49mpg overall.
Cannot comment on your idea about the tyres but I am getting a lot less that what I was led to believe from kia writeups and what the garage told me.

[AlanW55]

The Kia combined mpg for a old model 4 Hybrid on 18" wheels is 53.3, for ditto model 3 on 16" wheels is 58.9. So 18 " wheels are around 10% worse than 16" wheels, probably similar for new models. You're both citing driving in Autumn/Winter when mpg is generally lower, certainly true in my experience. Summer driving will improve your average figures. Maybe this explanation goes some way to answering your queries, but there are no definitive answers regarding mpg as we all drive differently.

[niro tyro]

Thanks for the response guys

[AlanHo]

I have a spreadsheet in which I record, every time I refuel the car, the date, exact amount of fuel added, the odometer reading and it calculates the mpg for each tank and the cumulative overall mpg since I bought the car.

My current 2021 GD 3 with 18" wheels has averaged 51.7 mpg over its 19,935 miles

My previous 2017 GD2, over its first 19912 miles, averaged 58.6 mpg

Hence in my case the difference in economy between the 18" wheels and 16" wheels is considerable even though my driving style and journey mix are the same.